The transmission of electrical power is a transfer of electrical energy generated by power plants to electrical substations located near demand centres via transmission lines. Such transmission lines might be interconnected with each other forming a transmission network. Such network is known as power grid, national grid or transmission grid, or just “the grid”. The grid interconnects large geographic areas, where a large number of power plants comprising generators deliver AC power with the same relative phase to a large number of consumers. These grids are operated by a control system comprising grid operators. The grid operator maintains the security of the grid by balancing the supply and the demand of energy to/from the grid. In order to achieve a stable balance between supply and load, the operator has to forecast the expected load and has to ensure, that enough power plants are available to supply the required energy to the grid. In order to ensure the required supply, the operator determines an optimal combination of power generating facilities and power reserve providers. The operator specifies which power plant out of the available power plants has to deliver which amount of energy in which period of time. The power plants offer amounts of energy they are able to supply in a market trading period and the operator specifies time and amount of energy to be delivered in a demand signal. If the supplied power deviates from the demand signal, the power plant will be charged from this deviation.
In the past large conventional power plants of typically more than 50 MW per power plant supplied the majority of the demanded energy to the grid. The daily load curve could be predicted very well, thus demand signals (power delivery schedule as a function of time) could be set-up 24 h in beforehand resulting in a reliable power supply and an easy manageable balancing control. The deviation of predicted demand and current supply remain small and could be compensated by slightly ramping-up or ramping-down of the conventional power plants. Conventional power plants are power plants generating the electrical power from thermal processes and are denoted as thermal power generation plants or facilities in the following, such as coal-fired, gas-fired or nuclear power plants.
Currently the amount of regenerative energy supplied to the grid by wind farms or photovoltaic plants increases significantly. The regenerative energy power plants provide a very fast response rate, however these power plants cannot guarantee to deliver a specified amount of energy at an appointed point of time in the future due to environmental uncertainties. The increased supply of regenerative energy to the grid results in a decreasing amount of predictable supply capacities of the contributing power plants provided by the so-called conventional or thermal power generation facilities (plants). In case of a short term decrease of regenerative energy due to less wind or less sunshine, the conventional power plants have to compensate the gap in short time. However typical conventional power plants have too slow response rates to compensate such gaps in short terms. Currently conventional power plants solve this issue be adapted turbines comprising steam valves or steam reservoirs.
US 2004/0020206 A1 discloses a steam turbine operated power plant comprising a primary and a secondary source of output power, where a large gas turbine is used to provide the majority of the demanded power having a lower response time and a small gas turbine to enable a faster ramping-up of the delivered power due to its faster response time until the large turbine takes over the power supply after having finished its ramping up phase. However when further increasing the amount of regenerative energies feeding the grid even the response rate of the small gas turbine will be too slow to compensate short term fluctuations of generative regenerative energy due to variations of the environmental conditions. Furthermore, the disclosed gas turbines cannot compensate overshoots of delivered energy compared to the demanded energy during operation of the conventional power plants, because such power sources cannot store energy.
For this reason it is desirable to provide a thermal power generation plant (conventional power plant) being able to reliable deliver the demanded power to the grid in accordance to any demand signal even in case of demand signals comprising steep rising and/or falling edges.